1. Field of the Invention
The present invention relates to a diode device, having both electrodes provided on a same surface thereof, capable of being directly connected to a conductive pattern on a circuit board without using lead wires.
2. Description of the Related Arts
Face-down bonding is a method for directly attaching integrated circuits to circuit boards such as printed boards and the like without using lead wires, conventionally used in the construction of various types of electronic circuits.
According to this method, electrodes are provided on the same surface of the integrated circuit, which is then turned face down and bonded directly to the circuit board. Since the integrated circuit consequently requires no packaging, the size of the integrated circuit can be scaled-down, lowering costs. For these reasons, face-down bonding is widely used.
However, although this method can be used for integrated circuits, chiefly provided with transistors, in which electrodes can be disposed on the same surface, it has not been possible to use face-down bonding in the case of diode devices having only two electrodes, such as, for instance, variable-capacity diodes.
FIG. 4 is a cross-sectional view illustrating a conventional variable-capacity diode device, in which region 3 and region 4, having different conductive types, are provided within an epitaxial layer 2 on a silicon semiconductor substrate 1, thereby forming a PN junction such as super abrupt junction.
In FIG. 4, 5 is an insulating film comprising silicon oxide, 6 is an electrode connecting to region 4, 15 is a lead wire, 16 and 17 are board-shaped terminals formed from lead frames.
Region 4 is exposed on the surface of the semiconductor main body which comprises the substrate 1 and the epitaxial layer 2, enabling an electrode to be provided on the surface of region 4. But, since region 3 lies beneath region 4, an electrode 18, which connects to region 3, is provided on the underside of the substrate 1.
The underside electrode 18 is securely joined to the terminal 16, by inserting a gold ribbon into the joint interface between the substrate 1 and the terminal 16 and applying heat thereto, a eutectic bond being formed of the terminal 16, the gold ribbon and the substrate.
The surface electrode 6 is connected to the terminal 17 by a gold lead wire 15.
The terminals 16 and 17 only are exposed to the outside, and packaging, such as a resin sealant, is provided. The terminals 16 and 17 are then connected to a circuit board.
Thus it has not been possible to connect the conventional diode device to a circuit board by means of face-down bonding since the two electrodes cannot be provided on the same surface.